There are many uses for large capacity batteries, such as starting automobile or boat engines, and, recently, supplying supplemental power to solar-power or wind-power systems. The storage batteries for these power systems may be used either as backups to the systems or to supply additional power during periods of peak need.
The batteries may sit for extended periods of time without use. For example, a battery which starts an engine on a sailboat is typically brought into service only when wind conditions adversely affect the progress of the sailboat along its desired route. Also, a battery which supplies supplemental power to a solar-power or wind-power system may be called upon sporadically, when weather conditions prevent the system from producing adequate power to meet ordinary demand or when demand exceeds the operating capacity of the system. In order for the batteries to be ready for this service, they must either be periodically charged or they must be able to retain their charge during the periods of non-use.
Batteries in some of these systems are charged whenever the systems are in use. For example, automobiles charge their batteries when the engine is in use. Accordingly, if the automobile is used relatively frequently, the battery retains its charge. Special arrangements must be made to charge batteries in other systems. For example, batteries for backup power systems are charged by diverting power from the system when the demand for power is relatively low. If demand does not reach a sufficiently low level, periodic charging may be impractical. Periodic charging of the batteries on sailboats may also be impractical, since the engines may be rarely used even though the boats are frequently in use. Accordingly, the charging may be forgotten, and thus, the batteries may be incapable of operating when they are most needed.
A prior invention of mine is directed to a battery which retains its charge during extended periods of non-use by separating the battery electrolyte from the battery electrodes, as described in my prior U.S. Pat. No. 4,439,501. This prior battery includes a system for providing to battery cells inert gas under pressure. The gas forces the electrolyte out of the battery cells and into a storage reservoir. The inert gas then remains in the cell to protect the electrodes from deterioration, for example, due to oxidation. To place the battery in service, the inert gas is released from the battery cells and the electrolyte is returned thereto under the force of gravity.
To form the storage reservoir, the prior battery includes an outer casing that essentially surrounds a conventional-size battery. The electrolyte is forced from the bottoms of the cells into this outer casing and, through somewhat circuitous channels, to a reservoir within the casing and above the cells. This prior battery has essentially two problems. First, the transfer rate of the electrolyte from the cells to the reservoir is relatively slow, unless the pressure of the gas is unacceptably high. The transfer rate of the electrolyte from the reservoir to the cells is also relatively slow, since the electrolyte returns under gravity along the circuitous channels. Second, the outer casing requires custom manufacture, which increases the cost of this battery. This casing also increases the over-all size of the battery, and thus, the battery may not fit into battery storage compartments.